Cyberpunk is more about unchecked power being dangerous than being anti-capitalism, in our history, most if not all crimes against humanity were commited by a state without checks and balances instead of a private company, but since Cyberpunk as a genre started in the 70s and 80s, megacorps were chosen as the villain, because those were the decades were technology had unprecedented advancements, and this new tech was being developed by private companies, the authors just took this concept and pushed to a comically exagerated degree, so much they truly believed we would have flying cars and become cyborgs by year 2000.
Even in universe, corporations can't reach their levels of power without first abusing the power of the state, they lobbied and elected officials in the city council to do their bidding.
I have no idea what's the solution or what's the perfect system, but blaming everything on capitalism (which is essentially the free trade of goods and services) is just a shallow interpretation of the setting with the intent of pushing a agenda.